Runway Guard Light – In-Depth Glossary

Runway Guard Light (RGL)

A Runway Guard Light (RGL) is a high-visibility, alternately flashing yellow lighting system installed at taxiway/runway intersections. Designed to warn pilots and ground vehicle operators of the presence of an active runway, RGLs are a vital part of the airport’s multilayered approach to runway safety. Commonly referred to as “wig-wags,” RGLs are typically positioned on both sides of the taxiway centerline at runway holding positions, ensuring that cockpit crews and ground vehicles receive a conspicuous, unambiguous visual warning before entering a runway.

The lights flash at a standard rate of 45–50 cycles per minute, as specified by ICAO Annex 14 and FAA regulations, optimizing human visual response. RGLs are engineered for all-weather operation—fog, rain, snow, or bright sunlight—using robust, corrosion-resistant materials and anti-glare visors. Their integration with Airfield Lighting Control and Monitoring Systems (ALCMS) allows for both manual and automated activation, as well as intensity adjustment depending on ambient light levels.

RGLs serve as a kinetic, active warning that complements passive aids such as painted hold markings and illuminated signage. They are a key safety feature at airports with complex taxiway/runway layouts, high traffic volumes, and historical runway incursion risks, and are mandated or recommended by international aviation authorities.

Wig-Wag

The Wig-Wag is the industry’s informal term for the elevated Runway Guard Light. It consists of two alternately flashing yellow lamps, mounted on frangible (breakaway) posts at each side of a taxiway holding position. The alternating flashes, reminiscent of a pendulum or “wig-wag” motion, are engineered to attract maximum attention and prompt pilots and ground vehicles to stop and verify ATC clearance before proceeding.

Wig-wags use high-intensity yellow LEDs or halogen bulbs, visible from up to 300 meters in all weather and lighting conditions. Their electrical systems are designed for reliability and redundancy, with fail-safe features and remote monitoring. Maintenance protocols include regular inspection, cleaning, and operational testing to ensure ongoing effectiveness.

In-Pavement Runway Guard Light

In-Pavement Runway Guard Lights are flush-mounted, unidirectional yellow lights embedded across the taxiway at runway holding positions. They are particularly effective where snow clearance, jet blast, or ground vehicle movement could interfere with elevated fixtures. Spaced at intervals of 1.5 to 3 meters, these lights create a continuous line of flashing yellow, ensuring high visual impact.

In-pavement RGLs use robust, weather-sealed LED or halogen technology to withstand aircraft wheel loads, de-icing chemicals, and heavy cleaning. The flash rate matches that of elevated wig-wags (45–50 cycles per minute). Integrated with ALCMS, they support remote status monitoring and intensity adjustment.

Runway Status Lights (RWSL)

Runway Status Lights (RWSL) are automated airfield lighting systems that use real-time surface surveillance data to provide direct, dynamic warnings to pilots and vehicle operators. RWSLs include Runway Entrance Lights (RELs) and Takeoff Hold Lights (THLs), which automatically illuminate when a runway is occupied or a potential conflict is detected, helping to prevent runway incursions without relying solely on ATC voice instructions.

RWSLs are integrated with airport surveillance systems and airfield lighting controls, offering a critical, automated layer of safety at busy airports. Their use is codified in FAA and ICAO standards and has been shown to significantly reduce runway entry errors.

Runway Entrance Light (REL)

Runway Entrance Lights (RELs) are red, in-pavement lights at runway/taxiway intersections, activated automatically when the runway is occupied or a conflict exists. RELs present a clear “stop” signal to pilots and drivers, overriding ATC clearance if necessary. Their robust, weatherproof design and automated operation are key to reducing runway incursions, especially at busy or complex airports.

Takeoff Hold Light (THL)

Takeoff Hold Lights (THLs) are red, in-pavement arrays placed parallel to the runway centerline at takeoff positions. THLs automatically illuminate when another aircraft or vehicle is detected on the runway ahead, providing a direct visual warning to hold position and not begin takeoff. Pilots are required by procedure to never initiate takeoff while THLs are illuminated.

Solar Runway Guard Light

Solar Runway Guard Lights are energy-autonomous RGLs powered by integrated solar panels and batteries. Designed for remote or infrastructure-limited airports, they use efficient LEDs and smart battery management to ensure reliable, all-weather operation. Solar RGLs reduce installation costs, minimize environmental impact, and provide backup during grid outages, supporting sustainability and safety objectives.

Airfield Lighting Control and Monitoring System (ALCMS)

An Airfield Lighting Control and Monitoring System (ALCMS) is a centralized platform for managing, monitoring, and diagnosing all airfield lighting, including RGLs and RWSL. It enables real-time status updates, remote adjustment, fault detection, and automated operations, ensuring optimal lighting performance and rapid maintenance response. Modern ALCMS platforms support remote access and cybersecurity, and are designed to meet ICAO and FAA specifications.

Runway Holding Position

A Runway Holding Position is a designated point on a taxiway—marked with parallel yellow lines and signage—where aircraft or vehicles must stop before entering or crossing an active runway. Enhanced with RGLs, illuminated signs, and sometimes stop bars, holding positions are critical locations for preventing runway incursions and are strictly enforced by international aviation regulations.

Taxiway Centerline

The Taxiway Centerline is a painted yellow line running along the center of a taxiway, guiding pilots and vehicles along the safest route between runways, ramps, and gates. At holding positions, the centerline may include dashed “lead-on” or “lead-off” markings. In airports with in-pavement RGLs or RELs, the lights are embedded directly along the centerline for maximum effectiveness.

Airport Surface Detection Equipment (ASDE)

Airport Surface Detection Equipment (ASDE) is ground-based radar or multilateration technology used to monitor and track all aircraft and vehicle movements on the airport surface. ASDE data drives automated lighting systems like RWSL, ensuring that visual warnings are synchronized with real-time surface conditions, and is a key enabler for advanced safety systems at major airports.

Surface Movement Guidance and Control System (SMGCS)

A Surface Movement Guidance and Control System (SMGCS) is an integrated system of procedures, visual aids, lighting, signage, and surveillance technologies that ensures the safe and efficient movement of aircraft and vehicles on the ground, especially in low-visibility conditions. SMGCS includes components like RGLs, stop bars, ASDE, and ALCMS, and is tailored to each airport’s unique layout and operational needs.

References

• International Civil Aviation Organization (ICAO) Annex 14, Volume 1: Aerodrome Design and Operations
• FAA Advisory Circular 150/5340-30: Design and Installation Details for Airport Visual Aids
• FAA Advisory Circular 150/5345-46: Specification for Runway and Taxiway Light Fixtures
• FAA Aeronautical Information Manual (AIM)
• https://www.faa.gov/airports/resources/advisory_circulars/
• https://www.icao.int/
• https://solutions4ga.com/solar-runway-guard-light/

A robust Runway Guard Light system is essential for maintaining runway safety and regulatory compliance at modern airports. By providing unmistakable visual warnings and integrating with advanced monitoring systems, RGLs help prevent runway incursions, protect lives, and support efficient airport operations.